How to change what modeline displays, based on major mode?

Question

i know i can change what info to display in modeline in mode-line-format variable. But how to display mode-line-position for one mode, but not display it for another?

Answer 1

Use (setq-local mode-line-position nil) in the mode-hook.

Example:

(define-derived-mode my-mode nil "my") ;; Our playground.

(defun remove-mode-line-position () ;; That's the thing you actually need.
  "Set `mode-line-position' buffer-locally to nil."
  (setq-local mode-line-position nil))

(add-hook 'my-mode-hook #'remove-mode-line-position) ;; Usage example.

If you create a new buffer with C-x b *mybuf* RET and call M-x my-mode RET the position info in the modeline disappears for buffer *mybuf* but for no other buffer.